The present invention relates to a sintered ceramic body comprising alumina and titanium nitride (Al.sub.2 O.sub.3 --TiN type) which has conventionally been produced by pressing at a high temperature such as hot pressing- or HIP process. Particularly, the present invention relates to a sintered ceramic body having an improved toughness and abrasion resistance, i.e. an improved cutting properties rather than Al.sub.2 O.sub.3 --TiN type ceramic tools.
It has been known that the Al.sub.2 O.sub.3 --TiN type ceramic tools obtained by sintering a mixture of 5-40% by volume of TiN and the balance of Al.sub.2 O.sub.3 by the hot pressing process (H.P. process) shows a relatively high resistance to oxidation and crater formation (Japanese Patent Application Open-laying No. 50-89410). However, since TiN per se has a hardness of Hv 2100 which stands lower than Hv 2700 of alumina per se, there have been some essential drawbacks in the abrasion resistance upon high speed cutting. Particularly, tips of such tools have been likely to chip off upon high speed intermittent cutting. A similar sintered ceramic body consisting of 5-15% by weight of TiN and the balance of alumina sintered by the hot-isostatic pressing process (HIP process hereinafter) is disclosed in Japanese Patent Application Openlaying No. 53-130208. This seramic tool showed some improvement in the abrasion resistance and thermal shock resistance. However, there is much to be desired particularly in the high speed cutting and the high speed intermittent cutting properties for the Al.sub.2 O.sub.3 --TiN type sintered ceramic bodies.
Furthermore, the sintering temperature of Al.sub.2 O.sub.3 --TiN system rapidly rises along with the increase of TiN content reaching about 1900.degree. C., which sintering temperature rise would inevitably cause an undesired crystal growth of alumina grain. Thus it has been difficult to obtain a sintered ceramic body which has above mentioned necessary properties as a high speed cutting tool.
Accordingly, the object of the present invention is to provide a novel sintered ceramic body and a novel manufacturing process thereof which can eliminate the drawbacks of the prior art.